1. Field of the Invention
This invention relates to gas turbines and more particularly to a flame monitor for scanning the combustion flame in one or more combustors to diagnose and control the operation of the gas turbine.
2. Description of the Prior Art
Gas turbines are used by electric utilities to drive generators to generate electricity. A gas turbine includes a number of combustors which are stationary and turbine blades which rotate on a rotor. The turbine blades are driven by the exhaust gases from the combustors. The combustors are fed with a fuel such as natural gas, or oil by fuel nozzles at one end of the combustors which ignite in the combustor forming a flame which has a recognizable pattern or signature. An air supply is also provided to the combustor to provide oxygen for combustion.
In the prior art it has been known to insert a viewing probe into the combustor to view the flame over angles from the outlet of the fuel nozzle to the exit of the combustor. A description of a viewing probe for monitoring a single combustor is described in U.S. Pat. No. 4,711,524 which issued on Dec. 8, 1987 by W. W. Morey et al. entitled "Combustor Fiberscope" and in a publication by A. C. Dolbec et al., entitled "Advanced Diagnostic Instrumentation For Combustion Turbines" proceedings of the American Power Conference, American Power Conference, Apr. 15, 1986, pages 1-7. A further description is provided in a paper by W. W. Morey and L. C. Angello entitled "Diagnostics from Imaging Inside Gas Turbine Combustors" presented at the International Society for Optical Engineering Meeting held at Quebec, Canada Jun. 4-6, 1986 and published in the Proceedings of SPIE "Optical Techniques for Industrial Inspection," Vol. 665, pp. 306-313. Further, an R&D status report was provided by L. C. Angello and G. H. Quentin, entitled "Gas Turbine Diagnostic Instrumentation", E.P.R.I. Journal, April/May 1986 pages 34-36 wherein an experimental monitoring system was installed in the hot gas path of a turbine was reported. The combustion viewing system used a video link to provide visual information on the flame in the combustor. An optical probe had a lens assembly with a wide angle (120.degree.-140.degree.) field of view to cover the extent of the combustor flame over a 356 millimeter (14 inch) combustor section. A subsequent R&D status report was given by L. C. Angello and G. H. Quentin entitled "Diagnostic Instrumentation for Combustion", E.P.R.I. Journal, July/August 1987 pages 38-40 wherein it was reported that the viewing probe demonstrated its usefulness in locating the combustor flame, determining its size, extension, and orientation; indicating light-off (ignition), flame-out, full-speed, no-load, and on-load conditions; and determining the presence of water injection, cross-fire flow, and intermittent water injection. Typical examples of combustor flame images with the fiber-optic viewing probe were also shown for a turbine during ignition, full-speed no-load condition, full-load condition and when water is injected for NO.sub.x control.
In U.S. Pat. No. 4,711,524 mentioned above a viewing lens is described comprising a sapphire doublet which is held internally in the probe with a viewing port at an opening in the end of the probe along the optical axis of the viewing lens.